U.S. patent number 6,172,882 [Application Number 09/469,276] was granted by the patent office on 2001-01-09 for partial resonance pwm converter.
This patent grant is currently assigned to TDK Corporation. Invention is credited to Kazuyuki Ito, Yoshihisa Okita, Katsuaki Tanaka.
United States Patent |
6,172,882 |
Tanaka , et al. |
January 9, 2001 |
Partial resonance PWM converter
Abstract
The present invention provide a partial resonance PWM converter
capable of making the switching loss occurring at a switch
approximately zero and high efficiency by controlling a switching
timing. A series circuit composed of upper and lower main switches
is connected in parallel with a DC power supply, and diodes are
respectively connected in parallel with each of the main switches
in the opposite direction of a polarity of the DC power supply. A
series circuit composed of upper and lower auxiliary switches is
connected in parallel with the DC power supply, and diodes are
respectively connected in parallel with each of the auxiliary
switches in the opposite direction of the polarity of the DC power
supply. A series resonance circuit composed of a capacitor and an
inductor is inserted between the juncture of the upper and lower
main switches and a juncture of the upper and lower auxiliary
switches. The switching timing is controlled to make the auxiliary
switch turn on just before the main switch is switched, to make the
main switch turn off during the diode connected in parallel with
each of the main switches is in ON condition, and to make the
auxiliary switch turn off during the ON condition of the diode
connected in parallel with each of the auxiliary switches.
Inventors: |
Tanaka; Katsuaki (Tokyo,
JP), Okita; Yoshihisa (Tokyo, JP), Ito;
Kazuyuki (Tokyo, JP) |
Assignee: |
TDK Corporation (Tokyo,
JP)
|
Family
ID: |
27285748 |
Appl.
No.: |
09/469,276 |
Filed: |
December 22, 1999 |
Foreign Application Priority Data
|
|
|
|
|
Dec 22, 1998 [JP] |
|
|
10-365185 |
Feb 4, 1999 [JP] |
|
|
11-027344 |
Mar 9, 1999 [JP] |
|
|
11-061328 |
|
Current U.S.
Class: |
363/17;
363/132 |
Current CPC
Class: |
H02M
7/5387 (20130101); H02M 7/4811 (20210501) |
Current International
Class: |
H02M
7/5387 (20060101); H02M 003/335 () |
Field of
Search: |
;363/16,17,132 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
BK. Bose, "Power Electronics AC Drives", pp. 131-140, Prentice
Hall, New Jersey, U.S.A., No Date..
|
Primary Examiner: Riley; Shawn
Attorney, Agent or Firm: Frishauf, Holtz, Goodman, Langer
& Chick, P.C.
Claims
What is claimed is:
1. In a partial resonance PWM converter including: a main switch
circuit composed of first and second main switch devices, said main
switch circuit being connected in parallel with a DC power supply;
diodes respectively connected in parallel with each of said main
switch devices in the opposite direction of a polarity of said DC
power supply; an output circuit located at a juncture of said main
switch devices;
an auxiliary switch circuit composed of first and second auxiliary
switch devices, said auxiliary switch circuit being connected in
parallel with said DC power supply; diodes respectively connected
in parallel with each of said auxiliary switch devices in the
opposite direction of the polarity of said DC power supply; and
a series resonance circuit composed of a capacitor and an inductor,
said series resonance circuit being inserted between the juncture
of said first and second main switch devices and a juncture of said
first and second auxiliary switch devices;
wherein said first and second main switches are alternatively
switched to output AC or DC power, said converter comprising,
control means for controlling a switching timing to make said
auxiliary switch device turn on just before said main switch device
is switched, and, at least in the main switch devices, to make said
main switch device turn off when said diode connected in parallel
with each of said main switch devices is turned nearly to ON
condition or during ON condition of said diode, whereby said main
switch device can be turned off at zero current, and to make one of
said main switch devices turn on during said first and second main
switch devices is in OFF condition and a load current passes
through said series resonance circuit, whereby a current passing
through said main switch device is increased from zero with having
a particular inclination so that said main switch device can be
turned on at zero current.
2. A partial resonance PWM converter as defined in claim 1, wherein
said control means is adapted to control a switching timing in said
auxiliary switch device to make said auxiliary switch device turn
off during ON condition of said diode connected in parallel with
each of said auxiliary switch devices.
3. In a partial resonance PWM converter including: a main switch
circuit composed of first and second main switch devices; a
capacitor circuit composed of first and second capacitors, wherein
said main switch circuit and said capacitor circuit are
respectively connected in parallel with a DC power supply; diodes
respectively connected in parallel with each of said main switch
devices in the opposite direction of a polarity of said DC power
supply;
a bi-directional switch device which is composed of two auxiliary
switch devices connected in series with each other and diodes
respectively connected in parallel with each of said auxiliary
switches; a series resonance circuit which is composed of an
inductor and a capacitor, wherein said a bi-directional switch
device and a series resonance circuit are inserted in series
between a connection point of said first and second main switch
devices and a connection point of said first and second capacitors;
and
an output circuit located at the connection point of said first and
second main switch devices; wherein said first and second main
switches are alternatively switched to output AC or DC power, said
converter comprising,
control means for controlling a switching timing to make said
auxiliary switch device turn on just before said main switch device
is switched, and, at least in the main switch devices, to make said
main switch device turn off when said diode connected in parallel
with each of said main switch devices is turned nearly to ON
condition or during ON condition of said diode, whereby said main
switch device can be turned off at zero current, and to make one of
said main switch devices turn on during said first and second main
switch devices is in OFF condition and a load current passes
through said series resonance circuit, whereby a current passing
through said main switch device is increased from zero with having
a particular inclination so that said main switch device can be
turned on at zero current.
4. A partial resonance PWM converter as defined in claim 3, wherein
said control means is adapted to control a switching timing in said
auxiliary switch device to make said auxiliary switch device turn
off during ON condition of said diode connected in parallel with
each of said auxiliary switch devices.
5. In a partial resonance PWM boost converter including: an
inductor and a main switch device which are connected in series
with a DC power supply; one terminal of an output capacitor
connected to a connection point of said inductor and said main
switch device via an output diode; another terminal of said
capacitor connected to a negative electrode of said DC power
supply; first diode connected in parallel with said main switch
device; first and second auxiliary switch devices which are
connected in series with each other, first and second auxiliary
switch being connected in parallel with said output diode; second
and third diodes respectively connected to the first and second
auxiliary switch devices in the opposite polarity with respect to
an output voltage; a series resonance circuit composed of a
resonance inductor and a resonance capacitor, said series resonance
circuit being inserted between a connection point of said first and
second auxiliary switch devices and a connection point of said
inductor and said main switch device; wherein, with making both
poles of said output capacitor an output, said main switch device
is switched by a PWM control so as to generate a stable DC voltage,
said converter comprising,
control means for controlling a switching timing to make said
second auxiliary switch device turn on just before said main switch
device is switched, and, in the main switch devices, to make said
main switch device turn off when said diode connected in parallel
with each of said main switch devices is turned nearly to ON
condition or during ON condition of said diode, whereby said main
switch device can be turned off at zero current.
6. A partial resonance PWM boost converter as defined in claim 5,
wherein said control means is adapted to control a switching timing
to make said main switch device turn on during all current of said
inductor passes through said series resonance circuit where the
current of said inductor is continuous during one switching cycle
of said main switch device, whereby a current passing through said
main switch device is increased from zero with having a particular
inclination to make the zero current turn-on possible.
7. A partial resonance PWM boost converter as defined in claim 5,
wherein said control means is adapted to control a switching timing
in said auxiliary switch device to make said auxiliary switch
device turn off when said diode, which is connected in parallel
with said auxiliary switch device, is in ON condition.
8. A converter comprising: first main switch device and second main
switch device which are connected in series with each other, said
first main switch device and second main switch device being
connected between first terminal and second terminal; third
terminal located at a connection point between said first main
switch device and second main switch device;
a series resonance circuit composed of a inductor and a capacitor,
which are connected in series, said series resonance circuit being
connected to a connection point between said first main switch
device and second main switch device; a diode having a forward
direction which directs from said second main switch device to said
first main switch device, said diode being connected in parallel
with each of said main switch devices,
wherein, with selecting either two of said first, second, and third
terminals as input terminals, a DC power supply is connected to the
two terminals selected as the input terminals;
a control means for generating an output between the output
terminals by alternatively switching said first and second main
switch devices; and
an auxiliary switch device where a resonance circuit is completed
jointly with said series resonance circuit by making it ON
condition when either one of said main switch devices is in ON
condition,
wherein said control means is adapted to control a switching timing
to make said main switch device turn off when said diode, which is
connected in parallel with said main switch device, is turned
closely to ON condition by the resonance current or during ON
condition of said diode, whereby the zero current turn-off of said
main device is made possible, and
said control means is adapted control a switching timing to turn on
said main switch device closely when, or after, a current passing
through said main switch device becomes zero by making the
resonance current run up to the value passing through said third
terminal with making said auxiliary switch device turn on just
before said main switch device is turned on to generate the
resonance current, whereby a current passing through said main
switch device is increased from zero with having a particular
inclination to make the zero current turn-on possible.
9. A converter as defined in claim 8, wherein said auxiliary switch
device includes first and second auxiliary switches, said first and
second auxiliary switches, which are connected in series with each
other, are connected between said first and second terminals, a
diode having a forward direction, which is a direction toward the
first terminal, is connected in parallel with each of said
auxiliary switches, said series resonance circuit is connected to a
connection point of said first and second auxiliary switches, and
said control means is adapted to control a switching timing to make
said auxiliary switches turn off when said diode, which is
connected in parallel with said auxiliary switch, is turned closely
to ON condition due to the resonance current passing through said
series resonance circuit when said auxiliary switch is turned on,
or during ON condition of said diode, whereby the zero current
turn-off of the auxiliary switches is made possible.
10. A converter as defined in claim 9, wherein said control means
is adapted to control a switching timing of said main switch device
and said auxiliary switch by a signal based on a current passing
through said series resonance circuit and a current passing through
said third terminal.
11. A converter as defined in claim 9, wherein said control means
is adapted to control a switching timing of said main switch device
and said auxiliary switch by a signal based on a voltage of both
ends of said main switch device.
12. A converter as defined in claim 8, further includes two
capacitors, which are connected in series with each other, being
connected between the first and second terminals, wherein said
auxiliary switch device is inserted between a voltage divided point
formed by said two capacitors and said series resonance circuit,
said auxiliary switch device is composed of a semiconductor switch
and a diode connected in parallel with said semiconductor, and said
control means is adapted to control a switching timing to make said
semiconductor switch of said auxiliary switch device turn off when
said diode, which is connected in parallel with said semiconductor
switch, is turned closely to ON condition due to a resonance
current passing through said series resonance circuit when said
semiconductor switch of said auxiliary switch device is turned on,
or during in ON condition of said diode, whereby said semiconductor
switch of said auxiliary switch device can be turned off at zero
current.
13. A converter as defined in claim 12, wherein said control means
is adapted to control a switching timing of said main switch device
and said semiconductor switch of said auxiliary switch device by an
current signal based on a current passing through said series
resonance circuit and a current passing through said third
terminal.
14. A converter as defined in claim 12, wherein said control means
is adapted to control a switching timing of said main switch device
and said semiconductor switch of said auxiliary switch device by a
signal based on a voltage of both ends of said capacitor of said
series resonance circuit.
Description
TECHNICAL FIELD
The present invention relates to a partial resonance PWM
converter.
PRIOR ART
Japanese Patent Laid-Open Publication Hei 6-284749 discloses an
inverter, wherein two main switches connected in series with each
other are connected in parallel with a DC power supply, two
auxiliary switches connected in series with each other are
respectively connected in parallel with these main switches, and a
connection point of the two main switches and a connection point of
the two auxiliary switches are connected with each other via an
inductor and a capacitor which are connected in series with each
other, so as to pick up an output at the connection point of the
two main switches. Diodes are respectively connected in parallel
with each of the main switches and the auxiliary switches in the
opposite direction of a polarity of the DC power supply. The
inverter described in this Laid-Open Publication intends to reduce
and inhibit the voltage surge and the switching loss which occur at
the main switch device, by taking advantage of a resonance current
generated from the series circuit composed of the inductor and the
capacitor. In this inverter, the main switch may be switched after
making a current through the main switch device zero by turning on
the auxiliary switch just before the main switch is switched. Thus
the voltage surge occurring at the main switch is inhibited and a
snubber circuit may also be omitted, thereby high efficiency and
low noise may be established. Herefrom, this inverter is referred
as a snubberless inverter in this Laid-Open Publication.
In the operation of this device, there is a problem that turn-on
loss and current surge/voltage surge can be caused from making the
main switch turn on at hard switching and also switching loss can
potentially be increased due to occurrence of the turn-off loss at
the auxiliary switch depending on a turn-off timing of the
auxiliary switch device.
As another prior art, there is "Novel Zero-Current-Transition PWM
Converter" described in "IEEE TRANSACTION ON POWER ELECTRONICS,
Vol.9, No.6, November 1994", page 601 to 606. This circuit includes
a basic circuit of a boost up converter wherein a main switch, with
which a diode is connected in parallel, and an inductor are
connected in series with a DC power supply, a connection point of
the inductor and the main switch device is connected to a negative
electrode of the DC power supply, and an output capacitor is
connected between the connection point and the negative electrode
via an output diode. A series resonance circuit composed of second
inductor and a capacitor, and an auxiliary circuit composed of an
auxiliary switch device, second diode and a third diode are
additionally incorporated in the basic circuit to allow the main
switch to be turned off at zero current so that voltage surge may
be controlled to reduce turn-off loss. In this circuit, the
auxiliary switch is turned on just before the main switch is turned
off so as to generate an resonance current. Then the diode
connected in parallel with the main switch device is turned on by
the generated resonance current. During the above course, the main
switch device is turned so as to make the zero current turn-off
possible. According to these actions, the voltage surge occurring
at the main switch device is controlled so that a snubber circuit
may be omitted and turn-off loss may also be reduced. Therefore a
partial resonance PWM boost converter characterized by high
efficiency and low noise can be constructed.
As a problem of this device, it is pointed that turn-off loss is
caused due to the fact that some current inevitably passes when the
auxiliary switch device is turned off. Further, in the case where a
continuous current is applied to the first inductor, a recovery
current of the output diode passes through the main switch device
when the main switch is turned on. This results in generated
turn-on loss and noise. Thus this type of circuit is limited in
facilitating high efficiency and low noise.
DISCLOSURE OF INVENTION
It is an object of the present invention to solve the problem
described above and to provide a partial resonance PWM boost
converter wherein, by controlling a switching timing of an
auxiliary switch device and a main switch device, the zero current
turn-on and zero current turn-off at the auxiliary switch device
and the main switch device can be achieved, and the switching loss
occurring at the main switch and the auxiliary switch can also be
made substantial zero, so that voltage surge and current surge can
be reduced to make the lower noise possible.
To achieve the aforementioned object, the present invention
provides a new converter. In this converter, a series circuit
composed of first and second main switch devices is connected in
parallel with a DC power supply, and diodes are connected in
parallel with each of the main switch devices in the opposite
direction of a polarity of the DC power supply. An output circuit
is located at a juncture of these main switch devices, and the main
switch devices are alternatively switched to output AC or DC power.
Another series circuit composed of first and second auxiliary
switch devices is connected in parallel with the DC power supply,
and diodes are connected in parallel with each of the auxiliary
switch devices in the opposite direction of the polarity of the DC
power supply. A series resonance circuit composed of a capacitor
and an inductor is inserted between the juncture of the first and
second main switch devices and a juncture of the first and second
auxiliary switch devices. The auxiliary switch is turned on just
before the main switch device is switched so as to generate a
resonance at the series resonance circuit. During resonance, at
least in the main switch devices, a switching timing is controlled
to make the main switch device turn off when the diode connected in
parallel with each of the main switch devices is turned nearly to
ON condition or during ON condition of the diode. Preferably, in
the auxiliary switch device, a switching timing may additionally be
controlled to make the auxiliary switch device turn off during ON
condition of the diode connected in parallel with each of the
auxiliary switch devices. This enables the main switch device and
the auxiliary switch device to be turned on at zero current and be
also turned off at zero current so that switching loss can be
reduced.
In another embodiment of the present invention, a series circuit
composed of first and second main switch devices and a series
circuit composed of first and second capacitors are respectively
connected in parallel with a DC power supply. Diodes are
respectively connected in parallel with each of the main switch
devices in the opposite direction of a polarity of the DC power
supply. Two auxiliary switch devices are connected in series
between a connection point of the first and second main switch
devices and a connection point of the first and second capacitors.
In this connection, a bi-directional switch device composed of the
auxiliary switches and diodes respectively connected in parallel
with each of the auxiliary switches, and a series resonance circuit
composed of an inductor and a capacitor are inserted in series.
With making the connection point of the main switch devices an
power output, the main switch devices are alternatively switched so
as to output an AC or DC power. In the converter according to this
embodiment, a switching timing is controlled to make the auxiliary
switch device turn on just before the main switch is switched, and
then to make the main switch device and the auxiliary switch device
turn on at zero current and also turn off at zero current by
detecting a current which passes through the main switch device and
the auxiliary switch device. Thus the switching loss can be reduced
and the noise caused from voltage surge and current surge can also
be reduced.
In other embodiment of the present invention, there is provided a
PWM boost converter, wherein an inductor and a main switch device
are connected in series with a DC power supply, one terminal of an
output capacitor is connected to a connection point of the inductor
and the main switch device via an output diode, and another
terminal of the capacitor is connected to a negative electrode of
the DC power supply, first diode is connected in parallel with the
main switch device, and, in some cases, first auxiliary switch
device is connected in parallel with the output diode. A series
circuit composed of first and second auxiliary switch devices is
connected in parallel with the output capacitor, and second and
third diodes are respectively connected to these the first and
second auxiliary switch devices in the opposite characteristic with
respect to an output voltage. A series resonance circuit composed
of a resonance inductor and a resonance capacitor is inserted
between a connection point of the first and second auxiliary switch
devices and a connection point of the inductor and the main switch
device, and, with making both ends of the output capacitor an
output, the main switch device is switched by a PWM control so as
to generate a stable DC voltage. Further a switching timing is
controlled to make the lower auxiliary switch device turn on just
before the main switch device is turned on so as to generate a
resonance current, and then to make the main switch device turn off
when the diode connected in parallel with the main switch device is
turned closely to ON condition by the generated resonance current
or during ON condition of the diode. This enables the main switch
device to be turned on at zero current. Additionally, in the case
where an inductor current is continuous during one switching cycle
of the main switch device, a switching timing is controlled to make
the main switch device turn on in the condition that all of the
inductor current passes through the series resonance circuit,
thereby no recovery current of the output diode passes through the
main switch device, and a current passing through the main switch
device is also increased from zero with having a particular
inclination to make the zero current turn-on possible. Further, in
the auxiliary switch device, a switching timing is controlled to
make the auxiliary switch device turn off when the diode, which is
connected in parallel with the auxiliary switch device, is in ON
condition, thereby it enables the auxiliary switch device to be
turned off at zero current. When the auxiliary switch device is
turned on, the resonance current is also increased from zero to
make the zero current turn-off possible.
According to the control mentioned above, both in the main switch
device and the auxiliary switch device, the zero current turn-on
and zero current turn-off can be achieved. In addition, the
switching loss can be reduced and the noise caused from voltage
surge and current surge can also be reduced.
In a converter according to further embodiment of the present
invention, first main switch device and second main switch device,
which are connected in series with each other, are connected
between first terminal and second terminal, and third terminal is
located at a connection point between the first main switch device
and second main switch device. A series resonance circuit composed
of a inductor and a capacitor, which are connected in series, is
connected to a connection point between the first main switch
device and second main switch device. A diode having a forward
direction, which directs from the second main switch device to the
first main switch device, is connected in parallel with each of the
main switch devices. With selecting either two of the first,
second, and third terminals as input terminals and also selecting
the remaining one and one of the input terminals as output
terminals, a DC power supply is connected to the two terminals
selected as the input terminals. This converter provides a control
means for generating an output between the output terminals by
alternatively switching the first and second main switch devices,
and an auxiliary switch device where a resonance circuit is
completed jointly with the series resonance circuit by making it ON
condition when either one of the main switch devices is in ON
condition. The control means controls a switching timing to make
the main switch device turn off when the diode, which is connected
in parallel with the main switch device, is turned closely to ON
condition by the resonance current or during ON condition of the
diode, so as to make the zero current turn-off of the main device
possible. The control means controls a switching timing to turn on
the main switch device closely when, or after, a current passing
through the main switch device becomes zero by making the resonance
current run up to the value passing through the third terminal with
making the auxiliary switch device turn on just before the main
switch device is turned on to generate the resonance current. Thus
a current passing through the main switch device is increased from
zero with having a particular inclination to make the zero current
turn-on possible.
The auxiliary switch device may include first and second auxiliary
switches. The first and second auxiliary switches, which are
connected in series with each other, may be connected between the
first and second terminals. It is preferable that a diode having a
forward direction, which is a direction toward the first terminal,
is connected in parallel with each of the auxiliary switches, and
the series resonance circuit is connected to a connection point of
the first and second auxiliary switches. The control means can be
adapted to control a switching timing to make the auxiliary
switches turn off when the diode, which is connected in parallel
with the auxiliary switch, is turned closely to ON condition due to
the resonance current passing through the series resonance circuit
when the auxiliary switch is turned on, or during ON condition of
the diode, so as to make the zero current turn-off of the auxiliary
switches possible.
The control means can also be adapted to control a switching timing
of the main switch device and the auxiliary switch by a signal
based on a current passing through the series resonance circuit and
a current passing through the third terminal. The control means can
also be adapted to control a switching timing of the main switch
device and the auxiliary switch by a signal based on a voltage of
both ends of the main switch device.
Furthermore in the present invention, two capacitors, which are
connected in series with each other, can be connected between the
first and second terminals, and the auxiliary switch device can be
inserted between a voltage divided point formed by the two
capacitors and the series resonance circuit. In this case, the
auxiliary switch device is composed of a semiconductor switch and a
diode connected in parallel with the semiconductor, and the control
means can be adapted to control a switching timing to make the
semiconductor switch of the auxiliary switch device turn off when
the diode, which is connected in parallel with the semiconductor
switch, is turned closely to ON condition due to a resonance
current passing through the series resonance circuit when the
semiconductor switch of the auxiliary switch device is turned on,
or during in ON condition of the diode. Thus, the semiconductor
switch of the auxiliary switch device can be turned off at zero
current.
In this case, the control means can be adapted to control a
switching timing of the main switch device and the semiconductor
switch of the auxiliary switch device by an current signal based on
a current passing through the series resonance circuit and a
current passing through the third terminal. The control means can
also be adapted to control a switching timing of the main switch
device and the semiconductor switch of the auxiliary switch device
by a signal based on a voltage of both ends of the capacitor of the
series resonance circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram showing a basic circuitry of a partial
resonance PWM converter according to the present invention.
FIG. 2 is a circuit diagram showing an example of a single phase
converter applied with a partial resonance PWM converter according
to the present invention.
FIG. 3 is a waveform diagram showing current/voltage waveform in
each part of a circuit shown in FIG. 2.
FIG. 4 is an enlarged diagram showing in a magnified form of a part
of the waveform shown in FIG. 3.
FIG. 5 is an enlarged diagram showing in a magnified form of the
remaining part of the waveform shown in FIG. 3.
FIG. 6 a circuit diagram showing a basic circuitry of a partial
resonance PWM converter according to another embodiment of the
present invention.
FIG. 7 is a circuit diagram showing an example of a single phase
converter applied with a partial resonance PWM converter shown in
FIG. 6.
FIG. 8 is a waveform diagram fully showing current/voltage waveform
in each part of a circuit shown in FIG. 7.
FIG. 9 is an enlarged waveform diagram showing front part of the
waveform shown in FIG. 8.
FIG. 10 is an enlarged waveform diagram showing rear part of the
waveform shown in FIG. 8.
FIG. 11 is a waveform diagram fully showing current/voltage
waveform in each part of a circuit shown in FIG. 7 according to
other example.
FIG. 12 is an enlarged waveform diagram showing front part of the
waveform shown in FIG. 11.
FIG. 13 is an enlarged waveform diagram showing rear part of the
waveform shown in FIG. 11.
FIG. 14 is a waveform of other example corresponding to FIG. 9,
where the example shown in FIG. 8 is modified in a part of control
method.
FIG. 15 is a waveform corresponding to FIG. 9, where the example
shown in FIG. 11 is modified in a part of control method.
FIG. 16 a circuit diagram showing other embodiment of a partial
resonance PWM converter according to the present invention.
FIG. 17 is a waveform diagram showing current/voltage waveform in
each part of the circuit shown in FIG. 16.
FIG. 18 is an enlarged diagram showing the waveform shown in FIG.
17.
FIG. 19 is an enlarged diagram showing the waveform shown in FIG.
17.
FIG. 20 a circuit diagram showing further embodiment of a partial
resonance PWM converter according to the present invention.
FIG. 21 is a waveform diagram showing current/voltage waveform in
each part of the circuit shown in FIG. 20.
FIG. 22 is an partial enlarged diagram showing the waveform shown
in FIG. 21.
FIG. 23 is an partial enlarged diagram showing the waveform shown
in FIG. 22.
FIG. 24 is a circuit diagram showing an example of another control
according to the present invention, with like manner as FIG. 2.
FIG. 25 is a circuit diagram showing an example of other control
according to the present invention, with like manner as FIG. 7.
FIG. 26 is a circuit diagram showing an example of further control
according to the present invention, with like manner as FIG.
20.
FIG. 27 is a circuit diagram showing a control in an example where
the position of the input/output terminal is varied from that in
FIG. 25, in a circuit similar to the circuit shown in FIG. 25.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter embodiments according to the present invention will be
described.
FIG. 1 shows a basic circuit as an embodiment of the present
invention. In FIG. 1, two main switch devices S1,S2, which are
connected in series with each other, are connected in parallel with
a DC power supply Vin. Two auxiliary switch devices S3,S4, which
are connected in series with each other, are also connected in
parallel with main switch devices S1,S2. Two connection points of
the main switch devices S1,S2 are connected to an output. An
inductor Lr and a capacitor Cr are connected between a connection
point of the main switch devices S1,S2 and a connection point of
the auxiliary switches S3,S4. A control circuit is provided for
controlling a switching timing of the main switch devices S1,S2 and
the auxiliary switches S3, S4. Diodes D1,D2,D3,D4 are respectively
connected in parallel with each of the main switch devices S1,S2
and the auxiliary switches S3, S4 in the opposite polarity with
respect to DC power supply Vin. A series resonance circuit composed
of the auxiliary switches S3,S4, inductor Lr and capacitor Cr
constructs an auxiliary circuit as opposed to a main circuit
including the main switch devices S1,S2. A power out is picked up
from an output circuit which is connected between the connection
point of the main switch devices S1 and S2 and the positive side or
negative side of the DC power supply.
FIG. 2 shows another embodiment of an inverter circuit according to
the present invention. FIG. 3 is a waveform diagram showing
switching motion of the present embodiment in the case where load
current Io passes in the direction of the arrow shown in FIG. 2.
FIG. 4 and FIG. 5 are enlarged diagrams of the waveform shown in
FIG. 3. In the circuit shown in FIG. 2, a bridge circuit composed
of main switch devices S1,S2,S5,S6 are connected in parallel with a
DC power supply Vin. Auxiliary switch devices S3,S4 are also
connected in parallel with the DC power supply Vin. A series
resonance circuit including an inductor Lr and a capacitor Cr is
inserted between a connection point of the main switch device S1
and the main switch device S2 and a connection point of the
auxiliary switch devices S3 and S4. Diodes D1,D2,D5,D6,D3,D4 are
respectively connected in parallel with each of the main switch
devices S1,S2,S5,S6 and the auxiliary switches S3, S4 in the
opposite polarity with respect to DC power supply Vin.
The main switch devices S1,S2 and the auxiliary switch devices
S3,S4 are switched at high frequency, and the main switch devices
S5,S6 are switched at low frequency. An output circuit A is
connected between a connection point of the main switch devices
S1,S2 and a connection point of the main switch devices S5,S6. A
load B is connected to an output terminal of the output circuit A
and an output power is picked up by this load B.
It is desirable for the main switch devices S5,S6 to apply BJT
having small conduction loss in order to reduce the loss occurring
at the main switch devices because the main switch devices involves
no increase of switching loss. It is also desirable for the main
switch devices S1,S2,S5,S6 to apply a semiconductor switch having
high speed switching ability, such as MOSFET, IGBT, and the like.
It may also apply a semiconductor switch having high speed
switching ability, such as MOSFET, IGBT, and the like, for the main
switch devices S1,S2,S5,S6 to apply. An output voltage is detected
at an output terminal of the output circuit A, and its signal is
input into an output voltage control circuit C. The output voltage
control circuit C generates an output signal SS0. The output
voltage control circuit C performs a PWM control for controlling
the pulse width of the output signal to make the output voltage to
be a sine wave. The output voltage control circuit C also generates
signals SS5,SS6 for driving the main switch devices S5,S6. In these
signal S5,S6, a switching frequency is equal to the frequency of
their output volt alternating current so that the switch devices
may be alternatively switched according to the polarity of the
output volt alternating current. Current detection circuits are
connected to the main switch devices S1,S2 and the auxiliary switch
device S3,S4. These current detection circuits output pulse signals
DS1,DS2,DS3,DS4 as a threshold current is zero.
A switching timing control circuit M is provided for controlling a
switching timing, and the signal SS0 and the signals
DS1,DS2,DS3,DS4 of the current detection circuit is input into this
control circuit M. The control circuit M outputs signals
SS1,SS2,SS3,SS4 for driving the main switch devices S1,S2,S3,S4
when the rise and fall of the signal SS0 and the signals
DS1,DS2,DS3,DS4 are input.
Hereat the switching timings of the switch devices will be
described with reference to FIG. 4 and FIG. 5 which are an enlarged
diagram of the waveform shown in FIG. 3. While a current
bi-directionally passes through the load, given that the load
current Io passes in the direction shown in FIG. 2, here. At this
moment, the main switch device S6 is in ON condition and the main
switch device S5 is in OFF condition. FIG. 4 shows a process
through which the main switch deviceS1 is turned off at zero
current, and the auxiliary switch device S3 is turned on and turned
off at zero current. Given that,Initially, the main switch device
S1 is in ON condition and a current IS1 equal to the load current
Io passes. All of the main switch device S2 and the auxiliary
switch devices S3,S4 are in OFF condition. At this moment, an
initial voltage value of the capacitor Cr is maintained in the
opposite polarity with respect to that shown in FIG. 2. When the
signal SS0 from the output voltage control circuit C raises at time
t0, the drive signal SS3 is raised by the signal SS0 as a trigger
to make the auxiliary switch device S3 turn on, in the switching
timing control circuit M. Then a resonance is initiated in a path
of the auxiliary switch device S3, the inductor Lr, the capacitor
Cr and the main switch device S1 according to the initial voltage
value of the capacitor Cr. At this moment, since a resonance
current Ir starts passing from zero in the auxiliary switch device
S3, the zero current turn-on is achieved in the auxiliary switch
device S3, thereby the turn-on loss becomes approximately zero.
When the resonance current Ir starts passing in the opposite
direction with respect to the direction of the arrow shown in FIG.
2, the current IS1 passing through the main switch device S1 starts
decreasing because it can be assumes that the load current Io is
approximately constant and the current IS1 is equal to a value
given by taking the resonance current Ir from the load current Io.
When the resonance current becomes equal to the load current Io at
time t1, the current IS1 passing through the main switch device S1
becomes zero. After time t1, the resonance current Ir becomes
larger than the load current Io so that a current may start passing
through the main switch device S1 in the opposite direction.
When the detection signal DS1 is raised by a current detection
device for setting the threshold current at zero and is input into
the switching timing control circuit, the drive signal SS1 is
raised by the rise of the signalDS1 as a trigger to make the main
switch device S1 turn off. Thus, in the main switch device S1, the
zero current turn-off is achieved so that the turn-off loss can be
approximately omitted.
After the main switch device S1 is turned off, the resonance
current passes through the diode D1. When a current at the diode D1
becomes zero at time t2, the resonance is terminated.
After elapsing a predetermined delay time from the pulse rise time
t1 of the detection signal DS1 of the current detection device, the
drive signal SS2 is raised at time t3 to make the main switch
device S2 turn on. At this moment, to make the main switch device
S2 turn on at zero current, this delay time period T1 to T3 is set
longer than the period t1 to t2. After time t2, since the load
current passes from the auxiliary switch device S3 through inductor
Lr and the capacitor Cr, the resonance current starts passing
through a path of the auxiliary switch device S3 inductor Lr and
the capacitor Cr when the main switch device S2 is turned on at
this timing (time t3 shown in FIG. 4). Since the resonance current
starts passing from zero, the zero current turn-on is achieved so
that the turn-on loss may become approximately zero.
During the period t2 to t3, the capacitor is charged by the load
current Io. An initial value of the resonance capacitor at the time
when the next resonance is started can be adjusted by controlling
the delay time period and adjusting this period. This enables the
amplitude of the resonance current to be adjusted so that the zero
current switching may be achieved all the time.
After time t3, a current given by adding the resonance current to
the load current passes through the resonance circuit. Then, at
time t4, the direction of the current IS2 passing through the main
switch device S2 is changed so that the detection signal DS2 of the
current detection device may be raised and be input into the
switching timing control circuit. The drive signal SS2 is fallen by
the detection signal DS2 as a trigger to make the main switch
device S2 turn off. At this moment, the main switch device is
turned off at zero current so that little or no turn-off loss may
occur.
When the resonance is advanced, the direction of the current
passing through the auxiliary switch device S3 is changed at time
t5. Whereat, the detection signal DS3 is raised and be input into
the switching timing control circuit. Then the drive signal SS3 is
fallen by the detection signal DS3 as a trigger to make the
auxiliary switch device S3 turn off. At this moment, the auxiliary
switch device is turned off at zero current so that little or no
turn-off loss may occur.
After time t5, the resonance current passes through the diode D3.
At time t6, the resonance current is blocked by the diode D3 to
terminate the resonance and the load current Io then passes through
the diode D2. At this moment, the voltage value of the capacitor Cr
is maintained in the polarity show in FIG. 2 and the value becomes
a initial value for the resonance to cause the next switching.
FIG. 5 shows a process through which the main switch means S1 is
turned on at zero current, and the auxiliary switch device S4 is
turned on and turned off at zero current.
Here, the main switch device S2 is in OFF condition and a current
IS2 equal to the load current Io passes through the diode D2 in the
opposite direction with respect to that of the arrow shown in FIG.
2. At this moment, an initial voltage value of the capacitor Cr is
maintained in the polarity shown in FIG. 2. When the signal SS0
from the output voltage control circuit falls, the drive signal SS4
is raised by the signal SS0 as a trigger to make the auxiliary
switch device S4 turn on, in the switching timing control circuit.
When the auxiliary switch device S4 is tuned on at time t7, a
resonance is initiated in a path of the capacitor Cr, the inductor
Lr, the auxiliary switch device S4, and the diode D2 according to
the initial voltage value of the capacitor Cr. At this moment,
since a resonance current starts passing from zero in the auxiliary
switch device S4, the zero current turn-on is achieved in the
auxiliary switch device S4, thereby the turn-on loss becomes
approximately zero.
The resonance current Ir passes in the direction of the arrow shown
in FIG. 2, the current given by adding the load current Io to the
resonance current Ir passes through the diode D2. When the
resonance is advanced, the direction of the current passing through
the auxiliary switch device S4 is changed at time t8. Then the
detection signal DS4 is raised and is input into the switching
timing control circuit. Then the drive signal SS4 is fallen by the
rise of the signalDS4 as a trigger to make the auxiliary switch
device S4 turn off. At this moment, in the auxiliary switch device
S4, the zero current turn-off is achieved so that little or no
turn-off loss may occur. After the auxiliary switch S4 is turned
off, the resonance current passes through the diode D4.
At time t9, the resonance current is blocked by the diode D2 to
terminate the resonance and then the load current Io passes through
a path of the diode D4, the inductor Lr, and the capacitor Cr.
After elapsing a predetermined delay time from the pulse rise time
t8 of the detection signal DS4 of the current detection device, the
drive signal SS1 is raised to make the main switch device S1 turn
on. In this case, this delay time period is set longer than the
period t8 to t9. When the main switch device S1 is turned on at
time t10, a path of the switch device S1, the capacitor Cr, the
inductor Lr and the diode D4 is created. Thus the resonance current
is reduced and a current passing through the main switch device S1
is increased. When the resonance current Ir is blocked by the diode
D4 to terminate the resonance, the load current Io passes through
the main switch device S1 at time 11. After the main switch device
S1 is turned on, the current IS1 of the main switch device S1 is
increased from zero with having a particular inclination by the
resonance current Ir. Thus the zero current turn-on at the main
switch device S1 is achieved so that the turn-on loss at the main
switch device S1 may become approximately zero.
The aforementioned control will be described in detail. In circuits
implementing the present invention, the resonance current is passed
by turning on an auxiliary switch device (e.g. the auxiliary switch
device S3) which is positioned at the same level as a main switch
device (e.g. the main switch device S1) through which the load
current passes, and the main switch device is then switched at zero
current created by the resonance current thereof. When the
auxiliary switch device is turned on, the capacitor Cr participated
in the resonance is charged at an initial voltage value for
performing the resonance. According to this initial voltage value,
the amplitude of the resonance current is varied so that a
condition for achieving the zero current switching can be realized.
In other words, if a voltage value, which is charged in the
capacitor Cr, complies with the formula as described below when the
auxiliary switch device is tuned on, the main switch device can
achieve the zero current switching. That is, after the auxiliary
switch is turned on, a diode, which is connected in parallel with
the main switch device, is turned on in the act of the resonance.
If the main switch device is turned on when the diode is turned
closely to such ON condition or during ON condition, the zero
current switching can be achieved so that the switching loss can
substantially be omitted.
Vcr.multidot.Io.multidot. (Lr/Cr) (1)
where,
Io is a load current value,
Lr is an inductance value,
Cr is a capacitance value,
Vcr is an initial voltage value of the capacitor Cr.
For making the initial voltage value of the capacitor Cr comply
with the aforementioned formula (1), the following control is
performed. That is, when the main switch device S1 is turned off,
there exists the period t2 to t3 during which both of the main
switch devices S1,S2 are turned off, as shown in FIG. 4. This
period corresponds to a condition where the load current Io passes
through the resonance circuit, and the resonance capacitor Cr is
charged by the load current Io. By making this period longer, the
charged voltage value of the capacitor Cr at time t6 when the
switching is completed can be increased so that the condition (1)
required for achieving the subsequent zero current turn-on at the
main switch device S1 can be satisfied. Further, when the main
switch device S1 is turned off, there exists the period t9 to t10
during which both of the main switch devices S1,S2 are turned off,
as shown in FIG. 5. During this period, the load current Io also
passes through the resonance circuit, and the resonance capacitor
Cr is charged by the load current Io. As shown in FIG. 5, when
making this period longer, the charged voltage value of the
capacitor Cr at time t1 when the switching is completed is
decreased due to the charging voltage polarity of the capacitor Cr
at time t9. By adjusting this period, the condition (1) required
for achieving the subsequent zero current turn-on at the main
switch device S1 can be satisfied.
When the load current passes in the opposite direction with respect
to that of the arrow shown in FIG. 2, the main switch device S5 is
in ON condition and the main switch device S6 is in OFF condition.
By controlling the switching timing as well as that described
above, all of the main switch devices S1,S2 and the auxiliary
switch devices S3,S4 can be turned off at zero current.
As described above, the switching loss can be made approximately
zero and the turn-on and turn-off can be also conducted at zero
current so that no voltage surge and no current surge may occurs
and the noise can significantly be reduced.
Another embodiment of the present invention will be described
hereinafter. FIG. 6 shows a basic circuit as an embodiment of the
present invention. In FIG. 6, two main switch devices S1,S2, which
are connected in series with each other, are connected in parallel
with a DC power supply Vin. Two capacitors C1,C2, which are
connected in series with each other, are connected in parallel with
main switch devices S1,S2. An input voltage from the input DC power
supply Vin is divided in half by these capacitors C1,C2. An
auxiliary circuit is connected between a connection point of the
capacitors C1,C2 and a connection point of the main switch devices
S1,S2. This auxiliary circuit comprises a circuit where auxiliary
switch devices S3,S4, which are bi-directional switches, an
inductor Lr and a capacitor Cr are connected in series with each
other. Diodes D1,D2,D3,D4 are respectively connected in parallel
with each of the main switch devices S1,S2 and the auxiliary switch
devices S3,S4. An output circuit is connected between the
connection point of the main switch devices S1,S2 and the positive
side or negative side of the DC power supply. The main switch
devices are alternatively switched by a PWM control so that a
stable DC voltage can be obtained.
FIG. 7 shows an embodiment of an inverter circuit according to the
present invention. FIG. 8 is a waveform diagram showing switching
motion of the present embodiment in the case where load current Io
passes in the direction of the arrow shown in FIG. 7. FIG. 9 and
FIG. 10 are enlarged diagrams of the waveform shown in FIG. 8.
As shown in FIG. 7, capacitors C1,C2, which are connected in series
with each other, are connected in parallel with a DC power supply
Vin. A half voltage as much as an input voltage from the DC power
supply is created at a connection point of the capacitors C1,C2. A
bridge circuit composed of main switch devices S1,S2,S5,S6 are
connected to the DC power supply Vin. Auxiliary switch devices
S3,S4, which are bi-directional switches, an inductor Lr and the
capacitor Cr are connected in series with each other, and they are
inserted between a connection point of capacitors C1,C2 and a
connection point of the main switch devices S1,S2 to construct an
auxiliary circuit. Diodes D1,D2,D5,D6,D3,D4 are respectively
connected in parallel with each of the main switch devices
S1,S2,S5,S6 and the auxiliary switches S3, S4 in the opposite
polarity with respect to a current passing through each switch
devices. The main switch devices S1,S2 and the auxiliary switch
devices S3,S4 are switched at high frequency, and the main switch
devices S5,S6 are switched at low frequency. An output circuit A is
connected between a connection point of the main switch devices
S1,S2 and a connection point of the main switch devices S5,S6. A
load is connected to an output terminal of the output circuit and
an output volt alternating current is picked up by this load. A
switching frequency of the main switch devices S5,S6 may be adapted
to be to a cycle of the output voltage and may apply BJT having
small conduction without any increased switching loss. The main
switch devices S1,S2,S5,S6 may also apply a semiconductor switch,
such as IGBT, MOSFET, BJT, and the like. In FIG. 7, IGBT is applied
to all switch devices. An output voltage is detected at the output
terminal of the output circuit, and its signal is input into an
output voltage control circuit C. The output voltage control
circuit C performs a PWM control and outputs a signal SS whose
pulse width is controlled to make the output voltage to be a sine
wave. In signals SS5,SS6 for driving the main switch devices S5,S6,
a switching frequency is equal to the frequency of their output
volt alternating current so that the switch devices may be
alternatively switched according to the polarity of the output volt
alternating current. Current detection circuits are connected to
the switch devices S1,S2,S3,S4. The current detection circuits
detect a current passing through the switch devices as a threshold
current is zero and output pulse signals DS1, DS2, DS3, DS4. A
control circuit M outputs signals SS1,SS2,SS3,SS4 for driving the
switch devices S1,S2,S3,S4 when the rise and fall of the signal SS0
and the signals DS1,DS2,DS3,DS4 are input.
Hereat the switching timings of the switch devices will be
described with reference to FIG. 8 and FIG. 9, 10 which are an
enlarged diagram of the waveform shown in FIG. 8. While a current
bi-directionally passes through the load, given that the load
current Io passes in the direction shown in FIG. 2, here. At this
moment, the main switch device S6 is in ON condition and the main
switch device S5 is in OFF condition.
FIG. 9 shows a process through which the main switch deviceS1 is
turned off at zero current, and the auxiliary switch devices S3,S4
are turned on and turned off at zero current. Given that Initially,
the main switch device S1 is in ON condition and a current IS1
equal to the load current Io passes. All of the main switch device
S2 and the auxiliary switch devices S3,S4 are in OFF condition. An
initial voltage value of the capacitor Cr is maintained in the
opposite polarity with respect to that shown in FIG. 7. When the
signal SS0 from the output voltage control circuit C raises, the
drive signals SS3,SS4 are raised by the signal SS0 as a trigger to
make the auxiliary switch device S4 turn on, in the switching
timing control circuit. Then a resonance is initiated in a path of
the auxiliary switch device S4, the diode D3, the inductor Lr, the
capacitor Cr, the main switch device S1 and the capacitor C1
according to the voltage value which is a difference between an
initial charged voltage value of the resonance capacitor Cr and a
voltage value of the capacitor C1 (Vin/2). At this moment, since a
resonance current Ir starts passing from zero in the auxiliary
switch device S4, the zero current turn-on is achieved in the
auxiliary switch device S4, and no resonance current passes through
the auxiliary switch device S3, thereby the turn-on loss becomes
approximately zero. When the resonance current Ir starts passing in
the opposite direction with respect to the direction of the arrow
shown in FIG. 7 and then the resonance current is increased larger
than the load current Io, the diode D1 is turned on. When the main
switch device S1 is turned off during the period t1 to t2, the zero
current turn-off is-achieved so that the turn-off loss can be made
approximately zero. In FIG. 9, when the current IS1 of the main
switch device S1 goes through near to zero, the output signal DS1
of the current detection device is fallen and is input into the
switching timing control circuit. The drive signal SS1 is fallen by
this signal as a trigger to make the main switch device S1 turn
off.
After the main switch S1 is turned off, the resonance current
passes through the diode D1. When a current at the diode D1 becomes
zero at time t2, the resonance through the main switch device S1
and the diode D1 is terminated. After time t2, both of IS1 and IS2
become zero current and the resonance current Ir and the load
current Io become even. When the main switch device S2 is turned on
at this period, the resonance starts passing through a path of the
main switch device S2, the capacitor C2, the auxiliary switch
device S4, the diode D3, the inductor Lr and the capacitor Cr.
Since the resonance current starts passing from zero, the zero
current turn-on is achieved so that the turn-on loss may become
approximately zero. In FIG. 9, the signal DS2 of the current
detection device is raised by detecting that a current at the main
switch device becomes near to zero and the signal is input into the
switching timing control circuit. The drive signal SS2 is raised by
this signal as a trigger to make the main switch device S2 turn on.
When the resonance through the main switch device S2 is advanced,
the diode starts to turn on at time t3. Thus, when the main switch
device S2 is turned on after time 3, the zero current turn-off is
achieved so that the turn-off loss may be made approximately zero.
In FIG. 9, when the current of the main switch device S2 goes
through near to zero, the output signal DS2 of the current
detection device is fallen and is input into the switching timing
control circuit. The drive signal SS2 is fallen by this signal as a
trigger to make the main switch device S2 turn off.
When the resonance is advanced, the polarity of the resonance
current Ir is changed at time t4. By detecting this, the output
signal DS3 of the current detection device is fallen. When the
resonance is further advanced, the polarity of the resonance
current Ir is changed again at time t5. By detecting this, the
output signal DS3 of the current detection device is raised and
this signal is input into the switching timing control circuit.
Then the drive signals SS3,SS4 are fallen by this signal as a
trigger to make both of the auxiliary switch devices S3,S4 turn off
simultaneously. At this moment, a current passing through the
auxiliary switch device S3 becomes approximately zero to achieve
the zero current turn-off and no current passes through the
auxiliary switch device S4 so that little or no turn-off loss may
occur. After time t5, the load current passes through the diode
D2.
FIG. 14 shows an embodiment modified in the control with respect to
the aforementioned control method. A difference from FIG. 9 is only
to omit a switching of the main switch device S2. In this
embodiment, the zero current turn-off at the main switch device S1
and the zero current turn-on and turn-off at the auxiliary switch
devices S3,S4 can be achieved.
FIG. 10 shows a process through which the main switch means S1 is
turned on at zero current, and the auxiliary switch devices S3,S4
are turned on and turned off at zero current, hereinafter. Given
that, Initially, the main switch device S2 is in OFF condition and
a current IS2 equal to the load current Io passes through the diode
D2 in the opposite direction with respect to that of the arrow
shown in FIG. 7. An initial voltage value of the capacitor Cr is
maintained in the polarity shown in FIG. 7. When the signal SS0
from the output voltage control circuit falls at time t6, the drive
signals SS3,SS4 are raised by the signal SS0 as a trigger to make
the auxiliary switch devices S3,S4 turn on simultaneously, in the
switching timing circuit. Then a resonance is initiated in a path
of the auxiliary switch device S4, the diode D3, the inductor Lr,
the capacitor Cr, the diode D2 and the capacitor C2 according to
the voltage value which is a difference between an initial charged
voltage value of the resonance capacitor Cr and a voltage value of
the capacitor C1(Vin/2). At this moment, since a resonance current
starts passing from zero in the auxiliary switch device S4, the
zero current turn-on is achieved in the auxiliary switch device S4,
thereby the turn-on loss becomes approximately zero.
The current IS2 given by adding the resonance current Ir to the
load current Io passes through the main switch device S2. Since the
resonance current Ir passes in the opposite direction with respect
to that of the arrow shown in FIG. 7, the current at the main
switch device S2 is decreased after time t6. Then the current IS2
at the main switch device S2 becomes zero, the resonance current Ir
and the load current Io become even. At this moment, when the main
switch device S1 is turned on, the resonance current at the main
switch device S1 starts passing from zero, thereby the zero current
turn-on is achieved so that little or no turn-on loss may occur. In
FIG. 10, when the current IS2 at the main switch device S2 becomes
zero at time t7, the signal DS2 of the current detection device is
raised and the signal is input into the switching timing control
circuit. The drive signal SS1 is raised by this signal as a trigger
to make the main switch device S1 turn on.
After time t7, a current value given by taking the resonance
current Ir from the load current Io passes through the main switch
device S1. When the resonance is advanced, the current IS1 at the
main switch device S1 becomes equal to the load current Io at time
t8 to make the polarity of the resonance current Ir change. At the
moment, the output signal DS3 of the current detection device
provided in the resonance circuit is fallen. Then, when the current
IS1 at the main switch device S1 becomes equal to the load current
Io at time t8 at time t9 and the polarity of the resonance current
moves to be changed, the signal DS3 of the current detection device
provided in the resonance circuit is raised and is input into the
switching timing control circuit. The drive signals SS3,SS4 are
raised by this signal as a trigger to make the auxiliary switch
devices S3,S4 turn off. At this moment, a current passing through
the auxiliary switch device S3 is approximately zero to achieve the
zero current turn-off and no current passes through the auxiliary
switch device S4 so that little or no turn-off loss may occur.
Hereinafter a condition for making the main switch device switch at
zero current will be described.
In this control method, the resonance current is passed by turning
on the auxiliary switch device, which is a bi-directional switch,
before the main switch device is turned on, and the main switch
device is then switched at zero current created by the resonance
current thereof.
When the auxiliary switch device is turned on, the capacitor Cr
participated in the resonance is charged at an initial voltage
value. According to a voltage value, which is a difference between
a half of the input voltage and the initial voltage of the
capacitor Cr participated in the resonance, and a characteristic
impedance value of the resonance circuit, the amplitude of the
resonance current is varied. This shows a clear understanding of
existence of a condition for achieving the zero current switching.
If a voltage value Vc, which is a difference between a half of the
input voltage and a voltage charged in the capacitor Cr, complies
with the formula (2) as described below when the auxiliary switch
device is tuned on, the main switch device can achieve the zero
current switching. That is, after the auxiliary switch is turned
on, a diode, which is connected in parallel with the main switch
device, is turned on in the act of the resonance. If the main
switch device is turned off when the diode is in ON condition, the
zero current switching can be achieved so that the switching loss
can substantially be omitted.
where,
Io is a load current value,
LR is an inductance value,
CR is a capacitance value,
As described above, according to this embodiment of the present
invention, all switching loss can be made approximately zero and
the turn-on and turn-off can be also conducted at zero current so
that no voltage surge and no current surge may occurs and the noise
can significantly be reduced.
In the inverter circuit of the embodiment shown in FIG. 7, another
embodiment performing a control different from the aforementioned
embodiment will be described hereinafter. While the same circuit as
the aforementioned embodiment is used with reference to FIG. 8
through FIG. 10 in the description of this embodiment, the same
effect can be obtained by modifying a switching timing. FIG. 11 is
a waveform diagram showing switching motion in the case where the
load current Io passes in the direction of the arrow shown in FIG.
7. FIG. 12 and FIG. 13 are enlarged diagrams of the waveform shown
in FIG. 11.
Hereat, a switching timing of the switch devices will be described
with reference to FIG. 12 and FIG. 13. While a current
bi-directionally passes through the load, given that the load
current Io passes in the direction shown in FIG. 2, here. At this
moment, the main switch device S6 is in ON condition and the main
switch device S5 is in OFF condition.
FIG. 12 shows a process through which the main switch deviceS1 is
turned off at zero current, and the auxiliary switch device S3,S4
is also turned on and turned off at zero current. Given that,
Initially, the main switch device S1 is in ON condition and a
current IS1 equal to the load current Io passes. All of the main
switch device S2 and the auxiliary switch devices S3,S4 are in OFF
condition. An initial voltage value of the capacitor Cr is
maintained in the opposite polarity with respect to that shown in
FIG. 7. When the signal SS0 from the output voltage control circuit
C raises at time t0, the drive signals SS3,SS4 are raised by this
signal as a trigger to make the auxiliary switch devices S3,S4 turn
on, in the switching timing control circuit. Then a resonance is
initiated in a path of the auxiliary switch device S4, the diode
D3, the inductor Lr, the capacitor Cr, the main switch device S1
and the capacitor C1 according to the voltage value which is a
difference between an initial charged voltage value of the
resonance capacitor Cr and a voltage value of the capacitor C1
(Vin/2). At this moment, since a resonance current starts passing
from zero in the auxiliary switch device S4, the zero current
turn-on is achieved in the auxiliary switch device S4, thereby the
turn-on loss becomes approximately zero.
When the resonance is advanced, the resonance current Ir and the
load current Io becomes even at time T1, and a current passing
through the main switch device S1 becomes zero. When the resonance
is further advanced after this, a current value given by taking the
load current Io from the resonance current Ir passes through the
diode D1, and the diode D1 keeps in ON condition during time t1 to
t2. When the main switch device S1 is turned off during the period
t1 to t2, the zero current turn-off is achieved so that the
turn-off loss can be made approximately zero. In FIG. 12, when the
current IS1 of the main switch device S1 goes through near to zero,
the output signal DS1 of the current detection device is fallen and
is input into the switching timing control circuit, The drive
signal SS1 is fallen by this signal as a trigger to make the main
switch device S1 turn off.
After the main switch S1 is turned off, the current, which is a
current value given by taking the load current Io from the
resonance current Ir, passes through the diode. When the resonance
is furthermore advanced, the resonance current Ir and the load
current Io becomes even again and a current at the diode D1 becomes
zero at time t2, the resonance through the main switch device S1
and the diode D1 is terminated. After time t2, since both of IS1
and IS2 are in OFF condition, both of the current IS1 and the
current IS2 becomes zero and the resonance current Ir and the load
current Io become even. When the main switch device S2 is turned on
at this period, the resonance starts passing through a path of the
main switch device S2, the capacitor C2, the auxiliary switch
device S4, the diode D3, the inductor Lr and the capacitor Cr.
Since the resonance current starts passing from zero, the zero
current turn-on is achieved so that the turn-on loss may become
approximately zero. In FIG. 12, the signal DS1 of the current
detection device is raised by detecting that a current at the main
switch device S1 becomes near to zero, and the signal is input into
the switching timing control circuit. The drive signal SS2 is
raised by this signal as a trigger to make the main switch device
S2 turn on.
When the resonance through the main switch device S2 is advanced
after time t2, the resonance current Ir and the load current Io
become even at time t3 and the diode starts to turn on. At time 3,
the main switch device S2 then starts to turn on, and a current
value given by taking the load current Io from the resonance
current Ir passes through. Thus when the main switch device S2 is
turned on after time t3, the zero current turn-off is achieved so
that the turn-off loss may be made approximately zero. In FIG. 12,
when the current of the main switch device S2 goes through near to
zero, the output signal DS2 of the current detection device is
fallen and is input into the switching timing control circuit. The
drive signal SS2 is fallen by this signal as a trigger to make the
main switch device S2 turn off.
When the resonance is further advanced, the resonance current Ir
becomes zero at time t4. By detecting this, the output signal DS4
of the current detection device is raised to make both of the
auxiliary switch devices S3,S4 turn off simultaneously. At this
moment, a current passing through the auxiliary switch device S4 is
approximately zero to achieve the zero current turn-off, and no
current passes through the auxiliary switch device S3 so that
little or no turn-off loss may occur. After time t4, the load
current Io passes through the diode D2.
In FIG. 15, an embodiment modified in the control with respect to
the aforementioned control method is shown. A difference from FIG.
12 is only to omit a switching of the main switch device S2. In
this embodiment, the zero current turn-off at the main switch
device S1 and the zero current turn-on and turn-off at the
auxiliary switch devices S3,S4 can be achieved.
Two current detection circuits are connected to an auxiliary
circuit with which the resonance inductor Lr, the resonance
capacitor Cr, the auxiliary switch device S3,S4 are connected in
series. Where the direction of the arrow of the resonance current
shown in FIG. 7 is positive, a threshold value of the signal DS3 is
set at a positive value near to zero and a threshold value of the
signal DS4 is set at a negative value near to zero. When setting at
such values, the signals DS3,DS4 have waveforms shown in FIG.
11.
FIG. 13 shows a process through which the main switch deviceS1 is
turned on at zero current, and the auxiliary switch device S3,S4 is
also turned on and turned off at zero current. The main switch
device S2 is in OFF condition and a current IS2 equal to the load
current Io passes through the diode D2 in the opposite direction
with respect to that of the arrow shown in FIG. 7. An initial
voltage value of the capacitor Cr is maintained in the polarity
shown in FIG. 7. When the signal SS0 from the output voltage
control circuit falls at time t5, the drive signals SS3,SS4 are
raised by this signal as a trigger to make the auxiliary switch
devices S3,S4 turn on simultaneously, in the switching timing
circuit. Then a resonance is initiated in a path of the diode D2,
the auxiliary switch device S4, the capacitor Cr, the inductor Lr,
the auxiliary switch device S3 and the diodeD4 according to the
voltage value which is a difference between an initial charged
voltage value of the resonance capacitor Cr and a voltage value of
the capacitor C1 (Vin/2). At this moment, since a resonance current
starts passing from zero in the auxiliary switch device S3, the
zero current turn-on is achieved in the auxiliary switch device,
and no resonance current passes through the auxiliary circuit S4,
thereby the turn-on loss becomes approximately zero.
After time t5, a current given by adding the resonance current Ir
to the load current Io passes through the diode D2. When the
resonance is advanced, a current passing through the diode D2
becomes zero, and the resonance current Ir and the load current Io
become even. When the main switch device S1 is turned on during
this period, a resonance current starts passing from zero in the
main switch device S1, the zero current turn-on is achieved,
thereby little or no turn-on loss occur. In FIG. 13, when the
current passing through the diode D2 becomes near to zero, the
output signal DS2 of the current detection device is raised and is
input into the switching timing control circuit. The drive signal
SS1 is raised by this signal as a trigger to make the main switch
device S1 turn on.
After time t6, a current given by adding the resonance current Ir
to the load current Io passes. When the resonance is further
advanced, the resonance current Ir becomes zero at time t7. Then,
the output signal DS3 of the current detection device provide in
the resonance circuit is raised, and this signal is input into the
switching timing control circuit. The drive signals SS3,SS4 is
raised by this signal as a trigger to make the auxiliary switch
devices S3,S4 turn off. At this moment, a current passing through
the auxiliary switch device S4 becomes approximately zero to
achieve the zero current turn-off, and little or no current passes
occur. Since the resonance current Ir passes in the direction of
the arrow shown in FIG. 7 and no current passes through the
auxiliary switch device S4 just before time t7, no turn-off loss
occur.
As described above, according to this embodiment, the zero current
turn-on and zero current turn-off in the main switch device and
auxiliary switch device can be achieved by detecting a current
passing through the main switch device and auxiliary switch device
to control a switching timing.
With reference to FIG. 16, other embodiment of the present
invention will be described hereinafter. A series circuit of an
inductor L1 and a main switch device S1 is connected to both ends
of a DC power supply Vin, and a series circuit of an output diode
D0 and an output capacitor C0 is connected to both ends of the main
switch device S1. A diode D1 is connected in parallel with the main
switch device S1, and an auxiliary switch device S2 is connected
with the output diode D0. A series circuit of an auxiliary switch
device S3 and an auxiliary switch device S4 is connected to both
ends of the output capacitor C0. Diodes D3,D4 are respectively
connected in parallel with each of the auxiliary switch devices
S3,S4 in the opposite polarity with respect to an output voltage. A
series resonance circuit composed of a resonance inductor Lr and a
resonance capacitor Cr is inserted between a connection point of
the auxiliary switch device S3 and the auxiliary switch device S4
and a connection point of inductor L1 and the main switch device
S1. With making the both ends of the output capacitor C0 an power
output, an output is a applied to a load resistance R0. An output
voltage value is detected from both ends of the output capacitor
C0, and such signal is input into an output voltage control
circuit. The output voltage control circuit performs a PWM control
for controlling the pulse width of a signal SS0 to obtain a stable
DC voltage. Current detection circuits are connected to the switch
devices S1,S2,S3,S4. The current detection circuits detect a
current passing through the switch devices as a threshold current
is set at near to zero and output pulse signals DS1, DS2, DS3, DS4.
A switching timing control circuit outputs signals SS1,SS2,SS3,SS4
for driving the switch devices S1,S2,S3,S4 when the rise and fall
of the signal SS0 and the signals DS1,DS2,DS3,DS4 are input.
MOSFET, IGBT, BJT, and the like can be applied as the switch
devices.
Hereat, with reference to waveform diagrams, the switching timings
of the switch devices as a control method for making the switching
loss approximately zero and also reducing the current surge and
voltage surge occurring upon switching will be described. FIG. 17
shows waveforms of each part during the time when the main switch
device is switched in one cycle, wherein a continuous current IL1
passes through the inductor L1 during one cycle.
FIG. 18 shows a process through which the main switch deviceS1 is
turned off at zero current, and the auxiliary switch devices S2,S4
are turned on and turned off at zero current. During the main
switch is in ON condition, the inductor L1 is excited to make an
inductor current IL1 pass through the main switch device S1 in the
direction of the arrow of IS1 shown in FIG. 16. All of auxiliary
switches S2,S3,S4 are in OFF condition. An initial voltage value of
the capacitor Cr is maintained in the opposite polarity with
respect to that shown in FIG. 2. When the signal SS0 from the
output voltage control circuit raises, the drive signal SS4 is
raised by this signal as a trigger to make the auxiliary switch
device S4 turn on, in the switching timing control circuit. Then a
resonance is initiated in a path of the auxiliary switch device S4,
the main switch device S1, the inductor Lr, and the capacitor Cr
according to an initial charged voltage value of the resonance
capacitor Cr. At this moment, since a resonance current Ir starts
passing from zero in the auxiliary switch device S4, the zero
current turn-on is achieved in the auxiliary switch device S4,
thereby the turn-on loss becomes approximately zero. After the
auxiliary switch device S4 is turned on, the resonance current Ir
starts passing in the opposite direction with respect to that of
the arrow shown in FIG. 6, and starts decreasing because it can be
assumes that the current IL1 of the inductor L1 is approximately
constant during a short period of switching and the current IS1 is
equal to a value given by taking the resonance current Ir from the
inductor current IL1. When the resonance current Ir becomes equal
to the inductor current IL1 at time t1, the current IS1 passing
through the main switch device S1 becomes zero. After time t1, the
resonance current Ir becomes larger than the inductor current IL1
so that the diode connected in parallel with the main switch device
S1 may be turned on during time t1 to t2 shown in FIG. 18. By
turning off the main switch device S1 during this period, the zero
current turn-off in the main switch device S1 is achieved so that
the turn-off loss can substantially be omitted. In FIG. 18, when
the current IS1 of the main switch device S1 goes through near to
zero, the output signal DS1 of the current detection device is
raised and is input into the switching timing control circuit. The
drive signal SS1 is fallen by this signal as a trigger to make the
main switch device S1 turn off.
After the main switch S1 is turned off, the resonance current Ir
keeps passing through the diode D1. When a current at the diode D1
becomes zero at time t2, the resonance is terminated.
After time t2, since the current IL1 of the inductor L1 passes
through a path of the resonance inductor Lr, the resonance
capacitor Cr, and the auxiliary switch device S4, the resonance
capacitor Cr is charged. An initial voltage value of the resonance
capacitor at the time when the next resonance is started can be
varied by adjusting the charging time period. This enables the
amplitude of the resonance current to be adjusted so that the zero
current switching may be achieved all the time.
When the auxiliary switch device S2 is turned on after time t2, the
resonance current starts passing through a path of the auxiliary
switch device S2, the resonance inductor Lr and the resonance
capacitor Cr and the auxiliary switch device S4. Since the
resonance current starts passing from zero, the zero current
turn-on in the auxiliary switch device S2 is achieved so that the
turn-on loss may become approximately zero.
In FIG. 18, a rise of the detection signal DS1 of the current
detection device is input into the switching timing control
circuit, the drive signal SS2 is raised by this signal as a trigger
after elapsing a delay time (t3-t1) so as to make the auxiliary
switch device S2 turn on. At this moment, the delay time(t3-t1) is
controlled to make it longer than the delay time (t1-t2), in the
switching timing control circuit.
When the auxiliary switch device S2 is turned on at time t3, the
resonance current passes in the opposite direction with respect to
that of the arrow of IS2 shown in FIG. 16. When the resonance is
advanced, the direction of the current IS2 passing through the
auxiliary switch device S2 at time t4 so that the detection signal
DS2 of the current detection device may be raised and then is input
into the switching timing control circuit. Then the drive signal
SS2 is fallen by the rise of the detection signal DS2 as a trigger
to make the auxiliary switch device S2 turn off. At this moment,
the auxiliary switch device S2 is turned off at zero current so
that little or no turn-off loss may occur. After time t4, the
output diode D0 is turned on and a current given by adding the
resonance current resonance current Ir to the inductor current
IL1.
When the resonance is advanced, the direction of the current
passing through the auxiliary switch device S4 is changed at time
t5. Then the detection signal DS4 of the current detection device
is raised and is input into the switching timing control circuit.
Then the drive signal SS4 is fallen by the rise of the signal DS4
as a trigger to make the auxiliary switch device S4 turn off. At
this moment, the zero current turn-off in the auxiliary switch
device S4 is achieved so that little or no turn-off loss may
occur.
Though the resonance current Ir passes through the diode D4
connected in parallel with the auxiliary switch device S4 after
time t5, the resonance current Ir is blocked by the diode D4 at
time t6 to terminate the resonance. Thus, after time t6, since the
inductor current IL1 passes through the output diode D0, an
exciting energy of the inductor L1 is transferred to the output
capacitor C0.
FIG. 19 shows a process through which the main switch means S1 is
turned on at zero current, and the auxiliary switch device S3 is
turned on and turned off at zero current.
The inductor current IL1 passes through the output diode D0. The
initial voltage value of the capacitor Cr is maintained in the
polarity shown in FIG. 16 by the resonance generated at the time
when the main switch device S1 is turned off. When the signal SS0
from the output voltage control circuit falls, the drive signal SS3
is raised by this signal as a trigger to make the auxiliary switch
device S3 turn on, in the switching timing control circuit. When
the auxiliary switch device S3 is tuned on at time t7, a resonance
is initiated in a path of the resonance capacitor Cr, the resonance
inductor Lr and the output diode D2 according to the initial
voltage value of the resonance capacitor Cr. At this moment, since
a resonance current starts passing from zero in the auxiliary
switch device S3, the zero current turn-on is achieved in the
auxiliary switch device S3, thereby the turn-on loss becomes
approximately zero.
The resonance current passes in the direction of the arrow shown in
FIG. 16 so that a current given by adding the inductor current IL1
to the resonance current Ir may pass through the diode D0.
When the resonance is advanced, the direction of the current
passing through the auxiliary switch device S3 is changed at time
t8. Then the detection signal DS3 is raised and is input into the
switching timing control circuit. Then the drive signal SS3 is
fallen by the rise of the signal DS3 as a trigger to make the
auxiliary switch device S3 turn off. At this moment, the auxiliary
switch device S3 is turned off at zero current so that little or no
turn-off loss may occur.
After time t8, the direction on the resonance current Ir is
inverted. Then the current given by adding the inductor current IL1
to the resonance current Ir is decreased and the current passing
through the diode D0 finally becomes zero at time t9. At this
moment, the detection signal DS2 of the current detection device is
fallen and the signal is input into the switching timing control
circuit. The drive signal SS1 is raised by the fall of detection
signal DS2 as a trigger to make the main switch device S1 turn on.
At time t9, all of the inductor current IL1 passes into the
resonance circuit. In this condition, when the main switch device
S1 is turned on, a path of the output capacitor C0, the diode D3,
the resonance capacitor Cr and the resonance inductor Lr is created
and then the resonance current Ir passing in the opposite direction
with respect to that of the arrow shown in FIG. 16 start
decreasing. That is, the current, which is a difference between the
inductor current IL1 and the resonance current Ir, is increased
from zero and this current passes through the main switch device
S1, thereby the zero current turn-on in the main switch device S1
is achieved so that the turn-on loss may become approximately
zero.
After the main switch device is turned on, the resonance current
becomes zero at time t10, and the inductor current IL1 passes into
the output capacitor C0 through the output diode D0.
Further embodiment of the present invention is shown in FIG. 20. In
this circuit, the auxiliary switch device S2 connected in parallel
with the output diode D0 and also the current detection device
outputting the signal DS2 are detached from the circuit shown in
FIG. 16.
Hereat, with reference to waveform diagrams, a control method for
making the switching loss approximately zero and also reducing the
current surge and voltage surge occurring upon switching will be
described. FIG. 21 shows waveforms of each part during the time
when the main switch device is switched in one cycle, wherein a
continuous current IL1 passes through the inductor L1 during one
cycle.
FIG. 22 shows a process through which the main switch device S1 is
turned off at zero current, and the auxiliary switch device S4 is
turned on and turned off at zero current. During the main switch is
in ON condition, the inductor L1 is excited to make an inductor
current IL1 pass through the main switch device S1 in the direction
of the arrow of IS1 shown in FIG. 20. An initial voltage value of
the capacitor Cr is maintained in the opposite polarity with
respect to that shown in FIG. 20. When the signal SS0 from the
output voltage control circuit raises, the drive signal SS4 is
raised by this signal as a trigger to make the auxiliary switch
device S4 turn on, in the switching timing control circuit. Then a
resonance is initiated in a path of the auxiliary switch device S4,
the main switch device S1, the inductor Lr, and the capacitor Cr
according to an initial charged voltage value of the resonance
capacitor Cr. At this moment, since a resonance current Ir starts
passing from zero in the auxiliary switch device S4, the zero
current turn-on in the auxiliary switch device S4 is achieved,
thereby the turn-on loss becomes approximately zero. After the
auxiliary switch device S4 is turned on, a current IS1 passing
through the main switch device S1 starts decreasing, and the
current IS1 passing through the main switch device S1 become zero
at time t1. After time t1, the diode D1 connected in parallel with
the main switch device S1 is turned on. By turning off the main
switch device S1 during this period, the zero current turn-off in
the main switch device S1 is achieved so that the turn-off loss can
substantially be omitted. In FIG. 22, when the current IS1 of the
main switch device S1 goes through near to zero, the detection
signal DS1 of the current detection device is raised and is input
into the switching timing control circuit. The drive signal SS1 is
fallen by this signal as a trigger to make the main switch device
S1 turn off.
After the main switch S1 is turned off, the resonance current Ir
keeps passing through the diode D1. When a current at the diode D1
becomes zero at time t2, the resonance is terminated. After time
t2, since the current IL1 of the inductor L1 passes through a path
of the resonance inductor Lr, the resonance capacitor Cr, and the
auxiliary switch device S4, the resonance capacitor Cr is
charged.
Then when a voltage of the resonance capacitor Cr exceeds the
output voltage, the resonance current Ir starts decreasing. At the
same time, the output diode D0 is turned on so that a current,
which is a difference between the inductor current IL1 and the
resonance current Lr, passes through the output diode D0.
When the resonance is advanced, the direction of the current IS2
passing through the auxiliary switch device S2 at time t4 so that
the detection signal DS2 of the current detection device may be
raised and then is input into the switching timing control circuit.
Then the drive signal SS2 is fallen by the rise of the detection
signal DS2 as a trigger to make the auxiliary switch device S2 turn
off. At this moment, the auxiliary switch device S2 is turned off
at zero current so that little or no turn-off loss may occur. After
time t4, the output diode D0 is turned on and a current given by
adding the resonance current resonance current Ir to the inductor
current IL1.
When the resonance is advanced, the direction of the resonance
current Ir passing through the auxiliary switch device S4 is
changed at time t3. Then the detection signal DS4 is raised and is
input into the switching timing control circuit. Then the drive
signal SS4 is fallen by the rise of the signal DS4 as a trigger to
make the auxiliary switch device S4 turn off. At this moment, the
auxiliary switch device S4 is turned off at zero current so that
little or no turn-off loss may occur.
After time t3, the resonance current Ir passes through the diode
D3. When the resonance is further advanced, the resonance current
is blocked by the diode D4 at time t4 to terminate the resonance.
After time t4, since the inductor current IL1 passes through the
output diode D0, an exciting energy of the inductor L1 is
transferred to the output capacitor C0.
FIG. 23 shows a process through which the main switch means S1 is
turned on at zero current, and the auxiliary switch device S3 is
turned on and turned off at zero current.
The inductor current IL1 passes through the output diode D0. The
initial voltage value of the capacitor Cr is maintained in the
polarity shown in FIG. 20 by the resonance generated at the time
when the main switch device S1 is turned off. When the signal SS0
from the output voltage control circuit falls, the drive signal SS3
is raised by this signal as a trigger to make the auxiliary switch
device S3 turn on, in the switching timing control circuit. When
the auxiliary switch device S3 is tuned on at time t5, a resonance
is initiated in a path of the resonance capacitor Cr, the resonance
inductor Lr and the output diode D2 according to the initial
voltage value of the resonance capacitor Cr. At this moment, since
a resonance current starts passing from zero in the auxiliary
switch device S3, the zero current turn-on in the auxiliary switch
device S3 is achieved, thereby the turn-on loss becomes
approximately zero.
The resonance current passes in the direction of the arrow shown in
FIG. 20 so that a current given by adding the inductor current IL1
to the resonance current Ir may pass through the diode D0. When the
resonance is advanced, the direction of the current passing through
the auxiliary switch device S3 is changed at time t6. Then the
detection signal DS3 is raised and is input into the switching
timing control circuit. Then the drive signal SS3 is fallen by the
rise of the signal DS3 as a trigger to make the auxiliary switch
device S3 turn off. At this moment, the auxiliary switch device S3
is turned off at zero current so that little or no turn-off loss
may occur.
After time t6, when the resonance is advanced and the current
passing through the diode D0 finally becomes zero at time t7, all
of the inductor current IL1 passes into the resonance circuit.
The switching timing control circuit is adapted to control to make
the main switch device S1 turn on after elapsing a time period
(t8-t5) from the auxiliary switch device S3 is turned on. At this
moment, the time period (t8-t5) is set to make it longer than the
time period (t7-t5), for performing the zero current switching.
When the main switch device S1 is turned on at time t8, a path of
the output capacitor C0, the diode D3, the resonance capacitor Cr,
and the resonance inductor Lr is created, and the resonance current
Ir passing with the same magnitude as the inductor current starts
decreasing. Thus the current IS1 passing through the main switch
device S1 becomes a value given by taking the resonance current Ir
from the inductor current IL1 and is increased from zero with
having a particular inclination, thereby the zero current turn-on
in the main switch device S1 is established so that the turn-on
loss may become approximately zero.
During the time period (t8-t7), the resonance capacitor Cr is
charged with the inductor current IL1 so that the initial voltage
value of the resonance capacitor Cr at the time when conducting a
subsequent resonance may be adjusted by this time period.
Therefore, the zero current switching can certainly be achieved by
setting a peak value of the resonance current Ir lager than the
inductor current IL1.
According to the control method as described above, in all of the
main switch device S1 and the auxiliary switch devices S3,S4, the
zero current turn-on and the zero current turn-off is made possible
so that the switching loss can be made approximately zero, no
voltage surge and no current surge may occurs, and the noise can
also be reduced.
In this control method, the resonance current is passed by turning
on the auxiliary switch device before the main switch device is
switched, and the main switch device can be switched at zero
current created by the resonance current thereof.
When the auxiliary switch device is turned on, the capacitor Cr is
remained at an initial voltage value. The amplitude of the
resonance current Ir is determined by the initial voltage of the
capacitor Cr and a characteristic impedance of the resonance
circuit. For achieving the zero current switching, it needs that,
after the auxiliary switch is turned on, the resonance current
should be equal to or larger than the inductor current IL1, and a
diode D1, which is connected in parallel with the main switch
deviceS1, should be turned on. Where Vc is the initial voltage
value of the resonance capacitor Cr at the time when the auxiliary
switch device is turned on, the condition for achieving the zero
current switching in the main switch device is given by the
following formula (3).
where,
IL1 is a maximum value of inductor current,
LR is an inductance value,
CR is a capacitance value,
Accordingly, the zero current switching can be achieved by setting
to make the initial voltage value of the resonance capacitor Cr
satisfy this condition.
FIG. 24 shows a modification of the circuit shown in FIG. 2. In
this circuit, there is provided a current detector in a serial
circuit composed of an inductor Lr and a capacitor Cr to generate a
current signal DS1a indicating a current passing through this
serial circuit. At the same time, there is provided another current
detector in an output line connecting between a connection point of
the main switch device S1,S2 and an output circuit A to generate a
current signal DS1b indicating a current passing through this
output line. In this case, a point where sum of two current signals
DS1a,DS1b is zero or approximately zero is set as a threshold. When
the sum of two current signals DS1a,DS1b cross over this threshold,
the main switch device S1 is turned off. According to this control,
the main switch device S1 can be turned off at zero current. In the
auxiliary switch device S3, a point where the current signal DS1a
is zero or approximately zero is set as a threshold. When the
current signals DS1a crosses over this threshold, the auxiliary
switch device S3 is turned off. According to this control, the
auxiliary switch device S3 can be turned off at zero current.
Hereinafter a control for making the main switch device turn on
will be described. When the main switch device is in OFF condition,
a current passing in the direction shown by arrow lo in the output
circuit A passes through the diode D2. The resonance capacitor Cr
is maintained at an initial voltage value. When the signal SS0 from
the output voltage control circuit C raises, the drive signal SS4
is raised by this signal as a trigger to make the auxiliary switch
device S4 turn on. As a result, a resonance current starts passing
in the direction shown as Ir. When the resonance is advanced, a
zero-cross that a current passing through the switch device S4
crosses over zero point is occurred. This zero-cross is indicated
by the detection output signal DS1a of the current detector which
is connected between the inductor Lr and the capacitor Cr. The
zero-cross is detected by making the detection output signal pass
through a comparator (not shown) to generate a detection signal.
The drive signal SS4 is fallen by the detection signal to make the
auxiliary device S4 turn off. After the aforementioned zero-cross
is occurred, the diode D4 connected in parallel with the auxiliary
device S4 is turned on. Thus, even when some time lag is occurred
in the turn-off timing of the auxiliary switch device, the
auxiliary switch device S4 can be turned off at zero current as
long as during the diode D4 is in On condition.
When the resonance is advanced, the resonance current and the
output current Io passing through the output circuit become even.
Thus the current IS1 passing through the main switch device S1 and
the current IS2 passing through the diode D2 become zero. As a
result, a voltage between both ends of the diode D2 starts
increasing. A control signal can be obtained by detecting the
voltage between both ends of the diode D2 and making this detection
signal pass through the comparator having the threshold in the
output voltage control circuit C. The drive signal SS1 is raised by
this control signal to make the main switch device S1 turn on. At
this moment, the current passing through the diode D2 becomes zero,
thereby no loss cased from a recovery current occurs. In addition,
the current passing through the main switch device S1 is increased
with having a particular inclination so that the zero current
turn-on of the main switch device S1 can be achieved.
FIG. 25 shows other example for switching at zero current with the
circuit as same as FIG. 7. The main switch devices S1,S2 and the
auxiliary switch devices S3,S4 are switched at high frequency, and
the main switch devices S5,S6 are switched at low frequency which
is the frequency as same as an output voltage waveform. An output
volt alternating current is generated at an output terminal of the
output circuit, and a signal detecting which is created by
detecting this output voltage is input into the output voltage
control circuit C. The output voltage control circuit C outputs a
square wave signal SS0 with duty ratio control, and this squared
wave signal is input into a switching timing control circuit M. The
switching timing control circuit M generates drive signals for
controlling the switch device S1,S2,S3,S4,S5,S6.
The current detector is provided in a series resonance circuit
composed of the inductor Lr and the capacitor Cr. The current
detector generates a current detection signal DS1 where the
opposite direction with respect to that shown by the arrow Ir is
defined as positive. For detecting a load current, a current
detector is provided in an output line from the connection point of
the main switch devices S1,S2 to an output circuit to generate a
current detection signal DS2 where the opposite direction with
respect to that shown by the arrow Io is defined as positive.
Further a voltage detector is provided for detecting a voltage of
both sides of the resonance capacitor Cr to generate a voltage
signal Vcr.
Operations of each switch device in this circuit are same as that
described in conjunction with FIG. 7. Therefore the detailed
description on the operation will be omitted, and the operation for
the zero current turn-off of the main switch device will be
described. Waveforms are shown in FIG. 12. Hereat, the auxiliary
switch device S3 and the main switch device S6 are in ON condition
during one cycle of the switching. When the main switch device S1
is in ON condition, the current Io passes through the main switch
devices S1,S6 in the direction of the arrow. The resonance
capacitor Cr is maintained at an initial voltage. In this
condition, when the control signal SS0 raises, the drive signal SS4
is raised by this signal as a trigger to make the auxiliary switch
device S4 turn on. At this moment, the resonance current Ir starts
passing in the direction of the arrow. As a result, a current
passing through the main switch device S1 starts decreasing. When
the resonance is advanced, the current at the main switch device S1
crosses over the zero-point and the sum of the current signals
DS1,DS2 also cross over the zero-point(hereinafter, refer to
zero-cross). The zero-cross is detected by making the signal, which
indicates the sum of the current signals DS1,DS2, pass through the
comparator having the threshold. Thus the drive signal SS1 is
fallen to make the main switch device S1 turn off.
After the current of the main switch device S1 and the signal
indicating the sum of the current signal DS1,DS2 cross over the
zero-point as described above, the diode D1 connected in parallel
with the main switch means S1 is in ON condition. Even when some
time lag is occurred in the turn-off timing of the main switch
device S1 due to control delay, the auxiliary switch device S4 can
be turned off at zero current as long as during the diode D1 is in
On condition.
When the resonance is advanced, the polarity of the resonance
capacitor Cr and the voltage signal Vcr of the both ends is
inverted. This inversion of the polarity of voltage signal is
detected by the comparator. Thus The drive signal SS2 is raised to
make the main switch device turn on.
When the resonance is further advanced, the resonance current Ir
passing through the series resonance circuit composed of the
inductor Lr and the resonance capacitor Cr cross over the
zero-point (hereinafter, refer to zero-cross). This zero-cross is
detected as the current signal DS1. Thus the drive signals SS3,SS4
are raised to make the auxiliary switch devices S3,S4 turn off.
Even when some time lag is occurred in the turn-off timing of the
auxiliary switch device S3,S4 due to control delay, the resonance
is terminated by the diode D3 so that the zero current turn-off in
the auxiliary switch device S3 can be achieved.
A control for making the main switch device S1 turn on at zero
current will be described hereinafter. Waveforms are shown in FIG.
13. In Off condition of the main switch device S1, the output
current Io passes through the diode D2 connected in parallel with
the main switch device S2 into to the output line in the direction
on the arrow, and the resonance capacitor Cr is maintained at the
initial voltage. Hereat, when the drive signal SS4 is raised, the
auxiliary switch device S4 is turned on and the resonance current
Ir starts passing in the direction shown by the arrow. When the
resonance is advanced, the current passing through the diode D2
starts decreasing and finally becomes zero. As a result, the
voltage of both ends of the diode D2 starts increasing. The voltage
between both ends of this diode D2 is detected. This detected
signal is passed through the comparator having the threshold in the
output voltage control circuit C so that the control signal can be
obtained. The drive signal is raised by this signal to make the
main switch means S1 turn on. At this moment, since the current
passing through the diode D2 becomes zero, no loss cased from a
recovery current occurs. In addition, the current passing through
the main switch device S1 is increased with having a particular
inclination so that the zero current turn-on of the main switch
device S1 can be achieved.
When the resonance is advanced, the zero-cross occurs in the
resonance current Ir. By detecting this zero-cross signal with the
comparator having the threshold, the drive signals SS3,SS4 are
raised to make the auxiliary switch devices S3,S4 turn off. Even
when some time lag is occurred in the turn-off timing of the
auxiliary switch device S3,S4 due to control delay, the resonance
is terminated by the diode D4 so that the zero current turn-off in
the auxiliary switch device S4 can be achieved.
FIG. 26 shows other example for performing the zero current
switching in the circuit shown in FIG. 20. First, a process through
which the main switch device S1 is turned off at zero current. When
the main switch device S1 is in ON condition, the input current IL1
passes through the main switch device S1. The resonance capacitor
Cr is maintained at an initial voltage. In this condition, when the
drive signal SS4 raises, the auxiliary switch device S4 is turned
on, and the resonance current Ir starts passing in the opposite
direction with respect to that of the arrow. As a result, a current
passing through the main switch device S1 starts decreasing. When
the resonance is advanced, the current IS1 at the main switch
device S1 crosses over the zero-point. At same time, the zero-cross
occurs in the current signal indicating the sum of the detection
signal DS1 of the input current and the detection signal DS2 of the
resonance current. By detecting this zero-cross, the drive signal
SS1 is fallen to make the main switch device S1 turn off. After the
zero-cross occurs in the current signal indicating the sum of the
zero-cross current signals DS1, DS2, the diode D1 connected in
parallel with the main switch device S1 is in ON condition. Thus,
even when some time lag is occurred in the turn-off timing of the
main switch device S1 due to control delay, the main switch device
S1 can be turned off at zero current as long as during the diode D1
is in On condition.
When the resonance is advanced, the zero-cross occurs in the
current passing through the switch device S4. This zero-cross is
detected as the current signal DS2. Hereat, the drive signals SS4
are raised to make the switch devices S4 turn off. After the
zero-cross occurs in the current of the switch device S4, the diode
D4 connected in parallel with the main switch device S4 is in ON
condition. Therefore, even when some time lag is occurred in the
turn-off timing of the main switch device S4 due to control delay,
the main switch device S4 can be turned off at zero current as long
as during the diode D4 is in On condition.
A process through which the main switch device S1 is turned on at
zero current will be described hereinafter. In Off condition of the
main switch device S1, the input current IL1 passes through the
diode D0 comprising the switch device, and the resonance capacitor
Cr is maintained at the initial voltage. Hereat, when the drive
signal SS3 is raised, the auxiliary switch device S3 is turned on.
Thus the resonance current Ir starts passing in the direction shown
by the arrow. When the resonance is advanced, the current passing
through the auxiliary switch device S3 crosses over the zero-point.
This zero-cross current is detected as the current signal DS2. Then
the drive signal SS3 is fallen by this signal to make the auxiliary
switch device S3 turn off. After the zero-cross occurs in this
current, the diode D3 connected in parallel with the auxiliary
switch device S3 is in ON condition. Therefore, even when some time
lag is occurred in the turn-off timing of the auxiliary switch
device S3 due to control delay, the auxiliary switch device S3 can
be turned off at zero current as long as during the diode D3 is in
On condition.
When the resonance is further advanced, the resonance current Ir
and the input current Ill become even so that the current passing
through the main switch device S1 and the current passing through
the diode D0 become zero. Therefore, the voltage between both ends
of the main switch device S1 starts increasing. This voltage
increase is detected by the comparator having the threshold so that
the drive signal may be raised to make the main switch device S1
turn on. At this moment, the current passing through the diode D0
becomes zero, thereby no loss occurs. In addition, the current
passing through the main switch device S1 is increased with having
a particular inclination so that the zero current turn-on of the
main switch device S1 can be achieved.
FIG. 27 shows further embodiment of a boost up converter according
to the present invention. In this embodiment, with using a circuit
as substantially same as that shown in FIG. 25, the position of the
input and output terminals is modified. That is, a terminal of
connection point of two main switch devices S1,S2 is applied to one
of input terminals and terminals of both ends of the main switch
devices S1,S2 are applied to output terminals. To detect the
resonance current, a current detector is disposed in a resonance
circuit composed of the inductor Lr and the capacitor Cr to create
a current signal DS2 where the arrow direction of the current Ir is
the positive direction. Another current detector is disposed in the
input line extending to the input terminal to create a current
signal DS1 where the arrow direction of the current Ii is the
positive direction.
In this circuit, a process through which the main switch device S2
is turned off at zero current will be described. Waveforms are same
as that shown in FIG. 9. However, the currents lS1,1S2 in FIG. 9
are respectively corresponding to the current IS2,IS1 in FIG. 27.
When the main switch device S2 is in ON condition, the current li
shown by the arrow on the input line passes through the main switch
device S2. The resonance capacitor Cr is maintained at an initial
voltage. In this condition, when the control signal SS0 from the
output voltage control circuit C is fallen, the drive signal SS4
from the switching timing control circuit M is raised by this
signal as a trigger to make the auxiliary switch device turn on. As
a result, the current passing through the main switch device S2 is
decreased by the resonance current Ir, results in the zero-cross
where the decreased current crosses over the zero-point. At the
sane time, the current signal indicating the sum of the current Ir
and The current Ii causes the zero-cross. The drive signal is
fallen by detecting this zero-cross current to make the main switch
device turn off. After aforementioned zero-cross occurs, the diode
D2 connected in parallel with the main switch device S2 is turn to
ON condition by the resonance current Ir. Therefore, even when some
time lag is occurred in the turn-off timing of the main switch
device S2 due to control delay, the main switch device S2 can be
turned off at zero current as long as during the diode D2 is in On
condition.
When the resonance is advanced, the polarity of the resonance
capacitor Cr and the both ends voltage Vcr is inverted. By
detecting this inversion of the polarity, the drive signal SS1 is
raised to make the main switch device S1 turn on. When the
resonance is further advanced, the resonance current Ir passing
through the auxiliary switch device causes the zero-cross. This
zero-cross is detected as the current signal DS2. Thus the drive
signals SS4 are raised to make the auxiliary switch devices S4 turn
off. In this case, according to the function of the diode D4
connected in parallel with the auxiliary switch device S4, the
auxiliary switch device S4 can be turned off at zero current as
long as during the diode D4 is in On condition.
A process through which the main switch device S2 is turned on at
zero current will be described hereinafter. However, the currents
IS1,IS2 in FIG. 10 are respectively corresponding to the current
IS2,1S1 in FIG. 27. In this case, the current of the input line
passes through the diode D1 connected in parallel with the main
switch device S1, and the resonance capacitor Cr is maintained at
the initial voltage. Hereat, when the control signal from the input
voltage control circuit C is raised, the drive signal SS4 is raised
by this signal as a trigger to make the auxiliary switch means S4
turn on. Thus the resonance current starts passing in the opposite
direction with respect to that of the arrow Ir.
When the resonance is advanced, the current IS1 passing through the
diode D1 starts decreasing. When this current IS1 becomes zero, the
voltage of both ends of the diode D1 starts increasing. The control
signal can be obtained by detecting the voltage of both ends of the
diode D1 and passing it through a comparator having a threshold in
the output voltage control circuit. The drive signal SS2 is raised
by this control signal to make the main switch device S2 turn on.
At this moment, the current passing through the diode D1 becomes
zero, thereby no loss cased from a recovery current occurs. In
addition, the current passing through the main switch device S2 is
increased with having a particular inclination so that the zero
current turn-on of the main switch device S1 can be achieved.
When the resonance is further advanced, the resonance current Ir
passing through the auxiliary switch device S4 causes the
zero-cross where the resonance current crosses over the zero-point.
This zero-point of the resonance current is detected as the current
signal DS2. The drive signal SS4 is raised in to make the main
switch device S4 turn off, response to this detection. By the
function ob the diode D4, even when some time lag is occurred in
the turn-off timing of the main switch device S4, the resonance is
terminated by the diode D4 so that the zero current turn-off in the
auxiliary switch device S4 can be achieved, as well as the
aforementioned embodiments.
While the present invention has been described with respect to
various specific example and embodiments, it is to be understood
that the present invention is not limited thereto, but only by the
claim.
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